1. Field of the Invention
The present invention relates to a scroll type hydraulic machine, and more particularly to a hydraulic machine preferably used as a compressor for a refrigerating circuit incorporated in an air conditioning system of a vehicle.
2. Description of the Related Art
This kind of scroll type compressor is provided with a housing, and a scroll unit arranged in the housing, and the scroll unit includes a stationary scroll and a movable scroll. These scrolls cooperate with each other so as to form compression chambers, and the compression chambers are intermittently connected to a refrigerating circuit, that is, a refrigerant circulating path.
In more detail, the movable scroll executes a revolving motion with respect to the stationary scroll in a state in which the movable scroll is inhibited from rotating on its own axis. The revolving motion of the movable scroll executes a series of processes from a suction of the refrigerant to the compression chamber from the circulating path to a compression and discharge of the refrigerant, and the discharged compression refrigerant is delivered to a condenser of the refrigerating circuit through the circulating path. In this case, the refrigerant sucked to the compression chamber is supplied from an evaporator of the refrigerating circuit.
Since a pressure of the refrigerant becomes very high in the compressing process of the refrigerant, the compressed refrigerant in the compression chamber applies a large reaction force, that is, a thrust force to the movable scroll. The thrust force operates so as to drag away the movable scroll from the stationary scroll, and hinders a smooth revolving motion of the movable scroll.
Accordingly, the compressor is provided with a thrust bearing supporting the movable scroll with respect to the housing, and the thrust bearing is disclosed, for example, in Japanese Unexamined Patent Publication No. 8-338377.
The thrust bearing in the publication includes a ring-like thrust plate, and this thrust plate is fixed to the movable scroll. The thrust plate is in sliding contact with a support surface of the housing so as to transmit a thrust fore to the housing during the revolving motion of the movable scroll.
Since a structure of the thrust plate is simple in comparison with a rolling bearing, the thrust plate is obtained inexpensively, however, can not sufficiently lower a sliding resistance of the movable scroll, so that an electric power consumption of the compressor is increased.
On the other hand, in the case that the scroll compressor is driven by an engine of a vehicle, the thrust load of the movable scroll is largely fluctuated on the basis of a rotating speed of the engine and a drive condition of the compressor.
Accordingly, it is necessary that this kind of thrust plate can sufficiently resist the great fluctuation of the thrust load. More specifically, the thrust plate is formed by a material having high hardness, and a sliding surface of the thrust plate in a side of the support surface is ground or coated. Therefore, the thrust plate has the sliding surface with a small friction coefficient. For example, the coating for the thrust plate is formed by nickel and phosphor plating, Teflon or the like disclosed in the publication.
The thrust plate mentioned above has an outer diameter which is approximately equal to that of the movable scroll, and is a comparatively large part in view of constituting parts of the compressor. Accordingly, since a lot of labor hour is required for grinding and coating the thrust plate, not only a productivity of the compressor is deteriorated, but also a cost of the compressor is increased.
Further, even if the sliding surface of the thrust plate is coated, a conjunction between the coating and a base material of the thrust plate is weak. Accordingly, the coating is peeled off from the thrust plate during the drive of the compressor, and the sliding resistance of the thrust plate is increased.